In the manufacture of semiconductor devices in recent years, there is an ever increasing tendency to use shorter wavelengths for the exposing light source in the associated exposure apparatus. The reason for this is that using shorter wavelengths raises the resolution of the projection exposure system and makes it possible to expose finer patterns. For example, since an F2 excimer laser has a short wavelength of 157 nm, application of this laser to exposure apparatus is proceeding. However, since exposing light produced by an F2 excimer laser is absorbed in an O2 or H2O environment, the space traversed by the exposing light must be purged using an inert gas.
Methods adopted to deal with this include a method of placing the overall exposure apparatus inside a tightly sealed chamber and a method of dividing the apparatus into several sections and purging each section.
In a case where the exposure apparatus is divided and purged, however, each individual section is controlled independently. A problem which arises is that a pressure difference develops between the sections and leads to deformation at the boundaries of these sections. Since these boundary areas consist of members that are transparent to the exposing light, even minute deformation of these members worsens the aberration of the exposing light.